1. Field of the Invention
The present invention relates to a surface treatment for a hot rolled metal using a fluidized bed system, in which a hot rolled metal is introduced into a gaseous fluidized bed having a non-oxidizing gas as a fluidizing medium. In addition the present invention relates to a surface treatment of the type described, conducted concomitantly with a patenting or cooling treatment.
2. Description of the Prior Art
In general, steel wire, rod or bar (referred to simply as steel wire rod, hereinafter) may be produced by a hot rolling process, then stored temporarily before delivery to a subsequent secondary working shop, where the steel wire rod is subjected to a descaling treatment such as pickling or the like, and then to a secondary working step such as heat treatment, plastic working or the like. The above manufacturing process, however, poses many formidable problems to be solved. For instance, wire rod produced in a mill shop can be subjected to a rust-preventive treatment to prevent rust on the wire rod during temporary storage or during transporation to the secondary working shop. However, besides the need for a costly rust-preventive agent, difficulties are encountered in positively preventing rust, which in itself gives rise to many problems. It is customary to subject hot-rolled steel wire rod to pickling to remove scales from the surface thereof, prior to the secondary working step. However, the above pickling process necessitates the use of costly equipment, required for preventing environmental pollution and for exhaust liquid treatment. In addition, steel wire rod is often subjected to a pretreatment for drawing, consisting of phosphating, or lime or borax coating, to improve the surface condition so that a lubricating agent can adhere to the surface in a secondary working step. This however, enhances the complexity of the secondary working.
The problems encountered with the secondary working of hot rolled steel wire rod stem from the surface condition of the wire rod, and hence the need persists for a method to improve the quality of the surface of steel wire rod.
Surface treatment of steel wire has generally included hot dipping and electroplating. The hot dipping process necessitates sophisticated techniques to control the thickness of the deposit, in addition to causing problems such as a low yield of the material to be used for hot dipping, and requires a large amount of thermal energy. On the other hand, the electroplating process results in an increase in the manufacturing cost.
Relevant prior art for the present invention is found in U.S. Pat. Nos. 3,560,239, 3,544,351, and 3,742,106, which disclose processes in which a powdered thermoplastic or thermosetting resin is coated on the surface of a substrate such as glass or steel wire or the like in a gaseous fluidized bed. A need, therefore, continues to exist for a method by which the shortcomings of the prior art surface treatment methods on hot rolled metal, particularly steel wire, rod or bar products, can be avoided.